President Trump said early Monday that he “NEVER told John Bolton that aid to Ukraine was tied to investigations into the Bidens or Democrats,” contrary to assertions Bolton reportedly made in the manuscript of his soon-to-be-published book, aptly titled, “The Room Where It Happened.”

The president’s tweet, just after midnight Monday, was his first reaction to a story in the New York Times about the forthcoming book by the president’s former national security adviser.

The book excerpt, and the leak, have the potential to increase pressure on the Senate to call witnesses in the impeachment trial of the president and, beyond that, to challenge the core defense of Trump, his lawyers and his supporters in Congress.

The Times reported late Sunday that, in the manuscript, Bolton writes of Trump telling him in August that “he wanted to continue freezing $391 million in security assistance to Ukraine until officials there helped him with investigations” into Democrats, including former vice president Joe Biden and his son Hunter Biden, who had been employed by a Ukrainian energy company.

That linkage is at the heart of the first article of impeachment against Trump, which alleges the president conditioned the aid to Ukraine and a visit to the White House by Ukrainian President Volodymyr Zelensky on the promise of an investigation that would serve to discredit a political rival.

Bolton’s reported claim, if true, would seriously undercut Trump’s attack on the reliability of the “abuse of power” charge. The president’s lawyers have argued that claims of linkage between the aid and the investigations have come only from people with second or third-hand information, who are making assumptions and presumptions but have never directly heard the president make any quid-pro-quo connection.

Bolton, as his book title suggests, says he was indeed in the room at a critical moment and that it did happen, according to the Times’ account.

Two people familiar with the manuscript, who spoke on the condition of anonymity because of its sensitivity, confirmed to The Washington Post that it details Trump tying aid to his desire for probes into the Bidens.

In his tweets and retweets early Sunday, Trump portrayed Bolton as a vengeful man just trying to sell books. He retweeted an apparent supporter comparing Bolton with former FBI director James B. Comey, who published a book after being fired by Trump. Besides, he tweeted, “the Democrat-controlled House never even asked John Bolton to testify. It is up to them, not up to the Senate.”

The retweets accused Bolton of “running the exact same revenge playbook … all because he’s mad Trump fired him for leaking and trying to start new wars.”

Bolton’s book appeared on Amazon overnight, available for preorder at $32.50 for the hardcover, $16.99 for the Kindle version and $39.99 for the audio CD, read by Bolton.

While trying to discredit the impeachment in the House and Senate, in part for lack of firsthand witnesses, Trump’s lawyers have simultaneously worked successfully to block any testimony by anyone who would have gotten close enough to fit that description.

Bolton, at times tauntingly, has said he is ready to testify if subpoenaed and he has plenty to testify about with regard to issues involved in the impeachment.

But a subpoena never arrived. The chances that it would were getting slimmer by the day as the Republican-controlled Senate appeared mostly unified in opposition to any witnesses.

With only a few days remaining in the Senate trial and acquittal a near-certainty, it was beginning to look like the whole proceeding would come to an end with Bolton’s secrets still concealed. People were beginning to wonder out loud and on social media whether any contents of the Bolton book would leak and, if so, whether that would happen in time.

On Dec. 30, Bolton submitted his manuscript to the White House for a standard review of potentially classified information, according to his lawyer, Charles J. Cooper. The White House could have, and still might, stand in the way of publication of portions of the book on national security grounds.

Sunday night, before that could happen, the leak occurred.

The Times account was sparse, mentioned no other elements of the book besides Ukraine, and it did not directly quote the unpublished manuscript, offering only a broad description. It said “multiple people described” Bolton’s account.

In addition to detailing Bolton’s account of what Trump told him — the linkage between the aid and the investigations — the Times said the manuscript portrays Attorney General William P. Barr and acting White House chief of staff Mick Mulvaney in a negative light.

“For example,” the Times said as it described the manuscript, “Secretary of State Mike Pompeo acknowledged privately that there was no basis to claims by the president’s lawyer Rudolph W. Giuliani that the ambassador to Ukraine was corrupt and believed Mr. Giuliani may have been acting on behalf of other clients."

“Mr. Bolton also said,” according to the Times, “that after the president’s July phone call with the president of Ukraine, he raised with Attorney General William P. Barr his concerns about Mr. Giuliani, who was pursuing a shadow Ukraine policy encouraged by the president, and told Mr. Barr that the president had mentioned him on the call. A spokeswoman for Mr. Barr denied he learned of the call from Mr. Bolton; the Justice Department has said he learned about it only in mid-August.”

“I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens,” Trump tweeted early Monday. “In fact, he never complained about this at the time of his very public termination. If John Bolton said this, it was only to sell a book.”

The report about the manuscript is fueling renewed demands by Democrats that witnesses, including Bolton, be subpoenaed to testify in the trial.

Among pro-impeachment lawyers, it also triggered discussions about alternatives to a full Senate vote on calling witnesses, which has been considered likely to fail.

Chief Justice John G. Roberts Jr., who is presiding over the Senate trial, “can easily subpoena these folks on his own,” and he “can’t even be overruled by Republicans in the Senate,” Neal Katyal, a former acting solicitor general, said on MSNBC on Sunday night.

In a New York Times op-ed Monday morning, Katyal, his Georgetown Law School colleague Joshua A. Geltzer and former congressman Mickey Edwards (R-Okla.) elaborated. They pointed to parts of the 1868 Senate rules of impeachment, still in force, that give the chief justice the power to issue subpoenas without being overruled by the Senate. Once a subpoenaed witness is deposed, and only then, the Senate has the final say on whether the witness also testifies.

Such an aggressive assertion of authority by the chief justice in a proceeding where he presides over a trial committed “solely” to the Senate by the Constitution would be extraordinary, deeply controversial and therefore unlikely.

But the story gave renewed hope to Democrats in the Senate and the prosecutors, or “managers,” representing the House that they might yet be able to sway enough Republican votes to get the subject of subpoenas on the floor for discussion, which is the first hurdle, and then issued.

This story has been updated.